c-api: implement wasm_tagtype_t for exception tag types (#10252) (#12763)

* c-api: implement wasm_tagtype_t for exception tag types (#10252)

Implement the C embedder API for WebAssembly exception t

c-api: implement wasm_tagtype_t for exception tag types (#10252) (#12763)

* c-api: implement wasm_tagtype_t for exception tag types (#10252)

Implement the C embedder API for WebAssembly exception tags, resolving
the long-standing todo!() in CExternType::new() that caused a Rust panic
whenever a module with tag exports had its exports enumerated via the
C API (e.g. wasm_module_exports / wasmtime_module_exports).

Changes:
- Add wasm_tagtype_t type with wasm_tagtype_new/params/delete/copy and
the standard as_externtype / externtype_as_tagtype cast functions
- Add WASM_EXTERN_TAG = 4 constant to wasm_externkind_enum in wasm.h
- Add CExternType::Tag(CTagType) variant; wire into CExternType::new()
and wasm_externtype_kind()
- Add wasmtime/types/tag.hh C++ wrapper (TagType / TagType::Ref)
- Extend ExternType::Ref variant and ref_from_c() switch in extern.hh
- Add TagType tests: construction, module export enumeration (regression
for #10252), and wasm_externtype_kind / cast function correctness

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* c-api: move tag type declarations to wasmtime/tag.h

- Revert wasm.h to its vendored upstream state (it must not be modified
locally; tag support is not yet in the upstream wasm-c-api spec header)
- Add crates/c-api/include/wasmtime/tag.h with wasm_tagtype_t forward
declaration, WASM_EXTERN_TAG constant, and all wasm_tagtype_* /
wasm_externtype_as_tagtype* function declarations
- Include wasmtime/tag.h from wasmtime.h

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Apply rustfmt and clang-format to tag type implementation

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Fix Clippy warnings: remove unused imports and dead code

Drop unused `wasm_tagtype_t` import from extern.rs, and remove the
`force`/`ty`/`wasm_tagtype_t::new` dead-code paths from tag.rs that
were written for future engine-resolution support but are not yet called.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

* Redesign tag type API with wasmtime_* prefix per reviewer feedback

- Rename wasm_tagtype_t → wasmtime_tagtype_t and all wasm_tagtype_*
functions → wasmtime_tagtype_* to avoid clashing with future wasm.h
additions (as requested by alexcrichton)
- Constructor now takes wasm_engine_t* + wasm_valkind_t array + count
instead of wasm_valtype_vec_t, eliminating the lazy-init complexity
- Replace wasm_tagtype_params() (returning a vec) with
wasmtime_tagtype_param_count() + wasmtime_tagtype_param(nth),
matching the component type accessor iterator pattern
- Rename WASM_EXTERN_TAG → WASMTIME_EXTERN_TAG
- Simplify CTagType: stores TagType directly, no Arc<Mutex<LazyTagType>>
- Update C++ TagType wrapper: constructor takes Engine&, Ref exposes
param_count() / param(nth) instead of params() returning ListRef
- Add ValType::c_to_kind() static helper used by TagType::Ref::param()
- Fix null-pointer panic for zero-length param arrays in Rust

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

---------

Co-authored-by: Claude Sonnet 4.6 <[email protected]>

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Move various C++ type-related items to their own header (#10627)

* Move C++ `ValType` to its own header

And fill out some small tests

* Move C++ `GlobalType` to its own header

* Move C++ `TableTy

Move various C++ type-related items to their own header (#10627)

* Move C++ `ValType` to its own header

And fill out some small tests

* Move C++ `GlobalType` to its own header

* Move C++ `TableType` to its own file

With some small tests

* Move C++ `FuncType` to its own file

* Move C++ ImportType to its own file

* Move C++ `ExportType` to its own file

* Move C++ `ExternType` to its own file

show more ...

Move C++ `MemoryType` to its own header (#10623)

While here fill out its API a bit with a builder type and some tests.